Wait for specific response, then execute next command

Since your proxy process runs in the background, the normal ways of capturing output don't work (ex: var=$(echo "test command"))

The easiest way to capture the output you want would be to redirect all output to a file, then check that file for the string you need.

Here's an example:

#!/bin/bash

set -m

# Added output redirection for stdout and stderr
./cloud_sql_proxy --add_your_options_here >filename 2>&1 &

# Wait for up to 5 seconds for the service to be ready.
for attempt in $(seq 1 5); do
    sleep 1
    if grep -q "Ready for new connections" filename; then
        break
    fi
    if [[ attempt -eq 5 ]]; then
        echo "Error launching sql proxy - see 'filename' for command output."
        exit
    fi
done

node app.js

To view output, cat filename.

This solution should work as long as the file is being truncated every time you run the script. If not, the grep will return true due to "stale" text in the file.